EDIT (as "No" is a bit blunt )
I've seen plenty of lads strip their cars to bare bones, and I think the onus is on the seats being safe if fitted, along with any safety restraints. The only required one being the driver's seat of course.
/EDIT
I was told once that the chip i had in my windscreen would be a fail, it would pass if beat the windscreen out
As for your seat, no worries there, take it in.
I built some specialist vans a while ago, no passenger seats.
the only time you would need the seats in is if its a minibus or any pcv vehicle where the seating capacity is registered on the mot which is in the form of a seat belt installation check and would be reduced if the seat had been removed
i thought if the vehicle was intended to be used with a given number of seats they had to be fitted...so if only one seat intended then only needs one, if you intend to fit more they need to be there for the safety checks.